Thermoelectric chiller and automatic syringe

ABSTRACT

An automatic syringe drive assembly and disposable heat exchanger cassette are used in combination to provide an improved thermodilution technique and apparatus. The automatic syringe drive assembly includes replaceable connecting rods on a slider crank mechanism which permit easy and accurate adjustment of the syringe injection volume. The drive assembly supports an insulated syringe for use in making the injection. The heat exchanger cassette includes a heat transfer plate and a thermoformed plastic labyrinth adhesively connected and used in combination with a thermoelectric chiller to provide a cold bolus of injectate.

This application is a continuation, of application Ser. No. 080,524,filed July 31, 1987, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a system for providing cold injectate to athermodilution cardiac output measuring catheter. Thermodilutioncatheters have been used to determine cardiac output and these cathetersare typically small diameter balloon types equipped with distaltemperature sensing means and a lumen opening a short distance proximalto the temperature sensor for introduction of a low-temperature liquidinjectate into the blood stream. The displacement of temperatureresulting from the introduction of the low temperature injectate issensed by the temperature sensing means, usually a thermistor. Suchsystems include a suitable supply of sterile injectate, usually 5%Dextrose in water or normal saline, and a multi-lumen catheter having atleast one lumen with a thermistor in it, another for injectate, and yetanother for a balloon. The injectate lumen has a proximal opening orport which is approximately 28 centimeters from the distal tip throughwhich the injectate is infused. There is a thermistor distal therefromand a balloon even more distal and finally a distal lumen.

The magnitude and duration of the temperature displacement over time canbe used to compute the blood flow rate for a measure of a patient'scardiac output. U.S. Pat. No. 3,995,623 shows a typical thermodilutioncatheter. The blood flow rate is computed from the displacement of bloodtemperature according to the Stewart-Hamilton dilution equation for athermal indicator as described in U.S. Pat. No. 3,987,788. As per thatprior patent, numerical values are used for a computation constant,blood temperature, and injectate temperature. The computation constantis derived from the nature of the injectate, the volume of the injectateand a correction factor for the rise in temperature of the 15 injectateas it passes through the lumen of the catheter to the injectate orifice.

Systems such as the Co-Set™from American Edwards Laboratories, SantaAna, California require that the injectate be supplied by a syringefilled from a coil of tubing placed in a container filled with crushedice. The ice covers the cooling coil of tubing and water is used toaffect heat transfer between the tubing and the ice. The container isinsulated styrofoam. Difficulties with thermodilution cardiac outputmonitoring include time wasted in loading the syringe, uncertainty ofthe syringe injectate temperature notwithstanding thermistors providedfor that purpose, inconsistent techniques which are a consequence of theclinicians misuse or unfamiliarity with the apparatus and concern aboutair bubbles in the system as a consequence of the filling of the syringeand then injection with the syringe.

U.S. Pat. No. 3,293,868 issued Dec. 27, 1966 to F. A. Gonzalez for"Fluid Cooling Apparatus" describes a device having a flat plate withsinuous-shaped upstanding fins which form a channel for holding a lengthof flexible tubing through which blood or the like can be passed forheating or cooling. The plate is in contact with a number of spacedthermocouples which operate by virtue of the thermoelectric effect toheat or cool the plate depending upon the direction current is passedthrough the thermocouples. A rotary blower may be further used to removeheat from the fluid. The device is designed to be used in a generallyhorizontal position with the blood or other fluid being forced throughthe tubing by a pump or the like. The apparatus lacks an automaticinjection system for easily and accurately delivered volumes of fluidand a simple disposable heat exchanger.

The Shah et al Patent No. 4,532,414 shows an inline fluid warmer forheating parenteral fluids such as blood. The warmer includes anenclosure containing a heated plate having a sinuously-shaped grooveconfigured to accept and hold the length of supply tubing in heattransfer relationship with the plate. Suitable temperature controls areprovided to regulate the heat and keep the blood at the preferred levelof heating. Good heat transfer in a disposable heat exchanger is nottaught.

Inconsistencies in injectate temperature and variations in injectiontechnique, such as injection speed or smoothness of the clinician cancause erroneous cardiac output measurements. These measurements couldpossibly result in inadvertent misdiagnosis and treatment which can bepotentially fatal. Also, injection of air bubbles into the pulmonaryvascular system is another potentially fatal situation due to thelikelihood of pulmonary embolism.

Motor actuated syringes have been subject of numerous prior art patents,for example, U.S. Pat. Nos. 3,336,925; 3,156,236; 3,335,724; 2,896,621;2,457,977; 3,313,291; 2,602,446; 2,498,672; and U.S. Pat. No. 3,584,623.However, none of these devices include an easily adjustable mechanismfor accurately varying the amount of volume injected.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a system that hasautomatic injection of easily varied standard volumes of cold injectate.

It is a further object of the present invention to provide athermoelectric cooling device for providing the chilled injectate.

It is still another object of the invention to have a simple,inexpensive disposable and efficient heat exchanger for use incombination with the thermoelectric cooler for the injectate.

SUMMARY OF THE DISCLOSURE

In order to overcome the problems of the prior devices and to teach asystem which includes all of the necessary elements to provide aconsistent, reliable, simple, and inexpensive arrangement which can beused without concern about variations in the skill level of theclinician, there is disclosed an automatically cooled injectatemechanism for use in combination with a cardiac output computer. Thesystem includes an automatic drive device for an insulated syringe witha disposable cassette heat exchanger. The syringe and the cassette canbe easily replaced in the basic system. Because of the disposablecassette and syringe, the basic mechanism of the system can be usedrepeatedly with different patients without concern of contamination ortransfer of disease or infection.

More specifically, the disposable portions of the system are designed tobe inexpensive and effective and easily used in combination with thebasic mechanism of the system. The basic system disclosed has anautomatic syringe driving mechanism which by merely changing aconnecting rod will provide various stroke volumes without concern forsophisticated levels of adjustment. In addition to this, there is aninjectate cooling device having a thermoelectric platen to which thedisposable heat exchanger cassette can be easily attached for coolinginjectate. The thermoelectric device is arranged to have intimatecontact with the conductive portion of the disposable heat exchangercassette such that cooling of injectate is uniformly, rapidly andefficiently accomplished. The temperature of the thermoelectricallychilled surface can be measured and used as input for the cardiac outputcomputer whereby the injectate temperature is properly controlled.

This system is simple, light weight and portable in that it does notrequire a supply of ice or water. The basic mechanism is arranged toclamp the heat exchanger cassette conductive portion against the chilledsurface of the thermoelectric cooler so that maximum surface contact isobtained and heat exchange takes place even though the heat exchangercassette is disposable and easily replaced. The clamping mechanism is adoor with a resilient nonconductive pad which acts not only as aninsulator but as a clamping device to hold the cassette against thethermoelectrically chilled surface.

The automatic injectate syringe driving system includes a gear-reducedmotor in combination with a slider crank mechanism, the connecting rodfor which is easily interchanged to increase or decrease stroke and,therefore, the injectate volume. In the preferred embodiment variousconnecting rod lengths are provided and are selected to drive thesyringe plunger in accordance with the stroke volume desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the automatic injection drive mechanismcomposed of a slider crank mechanism for the preferred embodiment.

FIG. 2 is a perspective view partially cut away of the disposable heatexchanger cassette of the preferred embodiment.

FIG. 3 is a top plan view with the housing in section showing theorganization of the disposable heat exchanger cassette and thethermoelectric device used to change the temperature of the injectatebolus.

FIG. 4 is a block diagram showing the relationship of the components inthe automatic injectate system of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1 is an automatic syringe drive assembly 10 which supports aninsulated syringe 11. The syringe 11 has a doubled wall insulatedsyringe barrel 12 and a plunger 13 which slides within the inner wall ofbarrel 12 of the syringe 11 to force fluids through the luer connector12a located at the distal end of the insulated syringe 11. In thecontext of this description distal means toward the luer connection 12aand proximal means in the opposite direction. At the proximal end of theinsulated syringe 11 are a pair of extending finger handles 14 which innormal or manual use are designed to fit the fingers of the syringeuser. In the application of the automatic syringe drive assembly 10, thesyringe 11 is held in a chassis 15 which is a heavy metal plate havingspecifically shaped openings to carry the components of the automaticsyringe drive assembly 10. In particular, there is a syringe barrelrecess 16 adapted and configured to support the insulated barrel 12against side to side or axial movement.

At the proximal end of recess 16 in chassis 15 is a transverse recess 17which extends outwardly from recess 16 to form a "T" shaped opening andto receive the handles 14. Adjustable tabs 18 are positioned parallel torecess 16 on each side thereof but spaced therefrom and each tab 18extends into a part of handle recess 17 to bear against and hold thefinger fitting portions of the handles 14. Adjustable tabs 18 can bemoved toward and away from the handles 14 to cause each handle 14 tobear against its more proximal side of the recess 17.

In order to drive the plunger 13 there is a flat slider 19 which isdriven by a connecting rod 20 rotated by a crank 21 at the connectingrod proximal end. The slider crank mechanism composed of the connectingrod 20, the crank 21 and the slider 19 converts the rotary motion of thecrank 21 to reciprocating motion of the slider 19. The reciprocatorymotion of slider 19 is controlled by guides 22 positioned within thechassis 15.

Specifically, the guides 22 have a groove arrangement for controllingthe motion of a tongue on each side of slider 19. The particularcomponents of the tongue and groove consist of chassis mounting channels23 located parallel to slider 19 and carried within chassis 15. Theguides 22 are received and supported in the operating plane of theinsulated syringe 11, the slider 19, and the crank 21 wherebyreciprocating motion of the slider 19 is in line with axis A--A of theplunger 13, see FIG. 1. Mounting channels 23 hold the guides 22 inposition for supporting the slider 19. There is a groove 24 in each ofthe guides 22 which controls the slider 19 for sliding reciprocatorymotion in line with the axis A--A of plunger 13. Each groove 24 isformed within its respective guide 22 by a pair of extending flanges 25designed to carry therebetween a tongue 26 extending transverse to andoutwardly from each of the sides of slider 19. Consequently, as slider19 reciprocates in response to forces transmitted through connecting rod20 a tongue 26 on each side of slider 19 moves within its respectivegroove 24. Motion of slider 19 is thus kept within the plane and axiallyrelative to plunger 13.

In the distal end of slider 19 is a "T" shaped opening 27 which receivesthe end 13a of the plunger 13 to permit movement of the plunger 13 inthe distal and proximal directions due to reciprocation of slider 19. Atthe proximal end of slider 19 is pin 28 which operates in a conventionalfashion to allow pivotal motion between the distal end of the connectingrod 20 and the slider 19.

Crank 21 is supported by a shaft in a known manner for rotation aboutthe crank center 29 in the direction shown by arrow B in FIG. 1. Chassis15 is stepped at wall 15a to provide clearance for moving parts, 19, 20and 21. The motor 34 is shown schematically in FIG. 1 but is actuallylocated beneath the chassis 15 to drive crank 21 about its center 29.Crank 21 has a series of threaded holes 21a positioned along a radiuswhich are used in cooperation with connecting rods of varying length.

P-1213 Longer connecting rods 20 in combination with the arrangementshown in FIG. 1 will provide a shorter plunger stroke. A replaceable pin20a connects the proximal end of connecting rod 20 to the crank 21. Pin20a is in the nature of a shouldered threaded fastener that can beunscrewed easily from the hole 21a allowing replacement of theconnecting rod 20 with another rod having a different length. The distalend of connecting rod 20 is designed to slip over the pin 28. Since themotion of slider 19 is kept in the plane of reciprocation by the tongueand groove arrangement 24, 25 and 26, no unseating forces are incurredat the connection of pin 28.

Crank 21 also includes a cam flat 21b which is used to control thestarting and stopping point for the syringe drive assembly 10. Shownschematically is a switch 30 having a cam movable contact 31 which isresponsive to cam flat 21b and a manually movable contact 32 such thatswitch 30 is normally closed except when movable contact 31 is againstcam flat 21b. When against the cam flat 21b the switch 30 is opened andthe circuit for the automatic syringe drive assembly 10 is disconnected.The manually operated contact 32 can be used to close switch 30 andstart the automatic syringe drive 10. The operating circuit includes apower supply 33, one leg of which is connected to movable contact 31 andthe other leg is connected to a motor 34 (shown schematically in FIG.1). The other input for motor 34 is connected to the fixed contact 32.

When the crank 21 is in the position of FIG. 1 and the cam flat 21b haspermitted moving contact 31 to break its connection from manuallyoperated contact 32, the motor 34 is disconnected from the power supply33. Consequently, switch 30 can be overridden to activate the automaticsyringe drive assembly 10. Switch 30 is designed to control the positionat which the slider 19 begins and ends its reciprocatory motion. Withthis arrangement the mechanism of the automatic syringe drive assembly10 can be manually started and automatically stopped for use inproviding one complete stroke. The plunger 13 begins and ends eachstroke at the same point, i.e. the most distal end of its travel withthe particular length of connecting rod used. The stroke of plunger 13is easily and accurately changed. The volume of injection is entirelyautomatic and easily and accurately set.

FIG. 2 shows the perspective view of a heat exchanger cassette 35 usedin connection with the automatic syringe drive assembly 10. The heatexchanger cassette 35 consists of a conductive plate 36 formed ofstainless steel sheet being 0.010 inches thick and measuringapproximately 2.75 inches by 4.375 inches. These dimensions can bevaried for the particular application and the stainless steel is asuitable grade and finish for medical use. Plate 36 is adhesivelyconnected to a thermoformed plastic labyrinth 37 which has repetitiveS-shaped convolutions. At the ends of the labyrinth 37 are specificallyshaped connectors 38 arranged to terminate the open ends of thelabyrinth 37. The labyrinth 37 consists of a channel 39 which isU-shaped in cross-section and forms a circuitous path by extending backand forth across beneath the plate 36 to form parallel passagewayshaving a hair pin turn at each end. The open ends of channel 39 arefilled with connectors 38 which convert the generally U-shaped channelcross-section to a circular cross-section forming male tubing extension40. A U-shaped portion 38a on each connector 38 is adhesively sealedinto an open end of channel 39 with an extended fitting portion 41.Through extended fitting portion 41 is a passage (not specificallyshown) carefully shaped to gently funnel the flow from the U-shapedchannel 39 to the circular cross-section of the male luer tubingextension 40.

Between each U-shaped channel 39 there are flat pad-like areas 39apositioned to rest against one of the major surfaces of the conductiveplate 36. Between the areas 39a and the plate 36 is placed hot meltadhesive 42 which seals the labyrinth 37 to the plate 36 forming a fluidtight circuitous conductive path through the U-shaped channel 39. Inparticular, at the ends of channel 39 are connectors 38 which permitfluid to flow from one end of the heat exchanger assembly 35 to theother. As will be explained in detail, fluid passing through thelabyrinth 37 formed by channel 39 exchanges heat. The volume of fluidcontained by the preferred heat exchanger 35 is at least three times thestroke volume of the automatic syringe drive 10. Heat exchanger 35 iseffective because the conductive plate 36 is metal and the labyrinth 37is plastic. The combination is easily constructed and efficient inoperation. It is also low cost, and, therefore, disposable. A safetyfeature is the hot melt adhesive 42 which cannot be autoclaved.Sterilization must be by radiation or ethylene oxide gas.

In operation the conductive plate 36 is held against the thermoelectricsurface of a chiller whereby fluid passing through the labyrinth 37 islowered in temperature to that of the conductive plate 36, see FIG. 3.In a preferred arrangement a thermoelectric chiller 44, having a finnedheat exchanger 45 with a series of junctions of dissimilar metals,causes the temperature of the finned heat exchanger 45 to change when acurrent is passed through the junctions. FIG. 3 is a top plan view ofthe arrangement for the thermoelectric chiller 44. More specifically,the way in which the disposable heat exchanger cassette 35 is brought tobear against the chilling surface of the thermoelectric chiller 44 isshown. The finned heat exchanger 45 is manufactured from an aluminumextrusion and is designed to support a chilled surface 46 which includesthe thermoelectric devices 46a that receive electrical current. Chilledsurface 46 can include a thin coating of electrical insulation such asceramic for safety. Depending upon the direction of electric currentflow through devices 46a, the temperature will increase or decrease. Inthe preferred application temperature decrease is used to chill thesurface 46. Opposite the cold surfaces of devices 46a heat is generatedand finned heat exchangers are used for heat removal. A fan assembly 47is provided to move air across the finned heat exchanger 45 and thuslower the temperature of the heat exchanger 45 to the ambient air.

A door 48 carried upon a hinge 49 is supported upon a housing 50 forheat exchanger 45. The combination of door 48, hinge 49 and housing 50permits easy replacement of the disposable heat exchanger cassette 35.The door 48 carries a resilient insulating foam pad 51 which is designedto bear against the labyrinth 37 of the heat exchanger cassette 35 andhold the conductive plate 36 against the chilled surface 46. Thedisposable cassette has a definitively configured surface 36 preferablyflat for intimate contact against complimentary surface 46 preferably aplaten. It should be appreciated that the heat exchanger assembly 35 isin the nature of a disposable medical device so that with each procedurea new cassette can be used without complications or difficulty. This isimportant to prevent transmission of infection. The connectors 38 havemale tubing extensions 40 which easily attach to the administration seton one end and the automatic syringe drive assembly 10 (at the luerconnection 12a) on the other end. For that purpose there is a specialtubing set which fits over extensions 40 and adapts to luer connections.

In order to hold the insulating foam pad 51 against the heat exchangercassette 35, there is a housing latch 52 which cooperates with the edgeof the door 48. In operation the chiller assembly 44 in combination withthe cassette 35 (as shown in FIG. 3) function to replace the normal coilof flexible tubing and ice bath used in the American Edwards Co-set™apparatus. That is to say that the arrangement schematically shown inFIG. 4 is known to medical practitioners except for the automaticsyringe drive 10, the chiller 44 and disposable cassette 35 which areherein shown and describe. The coil and ice bath are replaced with theapparatus of FIG. 3. All of the plumbing including valves andconnections are identical to that with which medical practitioners arefamiliar and that plumbing is arranged and used in accordance withconventional techniques. The apparatus of the present disclosureprovides automatic repetitive and adjustable chilling of a bolus and isaccurate, convenient and easy to use. In operation, the device of thepresent invention provides an accurately measured bolus at a preferredtemperature, both of which are readily and automatically controlled involume and temperature.

FIG. 4 is a block diagram of the automatic injection system 53 forpurposes of explaining how the automatic syringe drive assembly 10, thedisposable heat exchanger 35 and the thermoelectric chiller assembly 44are used. The injectate is drawn from an infusion set 54 into thecombination 55 which includes the thermoelectric chiller assembly 44 anddisposable heat exchanger cassette 35. The operation of the syringedrive assembly 10 can be automatically controlled by a cardiac outputcomputer 56 which is electrically connected to the automatic syringedrive assembly 10 and the combination 55 of disposable heat exchanger 35and thermoelectric chiller assembly 44. Once the temperature of theinjectate drawn from the infusion set 54 has reached the propertemperature, a signal is transmitted from the combination 55 to thecomputer 56 and in response thereto the automatic syringe drive assembly10 is activated by means of its electrical connection to computer 56.

The flow of injectate as pumped by the syringe drive assembly 10 iscontrolled by check valves 57. The check valves 57 are arranged topermit fluid to first flow from the infusion set 54 to fill thecombination 55 and then from there to thermodilution catheter 58. Morespecifically, the syringe drive assembly 10 is first filled from theinfusion set 54 and then the syringe plunger 13 forces the injectateback through check valves 57 and into the thermodilution catheter 58.The check valves 57 are merely two one-way valves which permit flow fromthe infusion set 54 through the combination 55 (filling disposable heatexchanger cassette 35 and syringe drive assembly and then from theautomatic syringe drive assembly 10 and combination 55 to thethermodilution catheter 58.

The thermodilution catheter 58 is placed within the patient. In thepatient end of the thermodilution catheter 58 is a thermistor which iselectrically connected to the cardiac output computer 56 such that thetemperature of that portion of the catheter can be monitored by thecardiac output computer.

To operate the combination 55 is electrically activated and filled withinjectate by cycling syringe drive assembly 10. The automatic syringedrive assembly 10 is run through one cycle such that a volume ofinjectate is drawn from the infusion set 54 and purged through thesystem. During the purge the ambient injectate within the system isdelivered to the patient. The volume of the disposable heat exchangercassette 35 is at least three times that of one stroke of the syringeplunger 13. Therefore, the purge cycle is adequate to deliver all of theambient injectate into the patient and leave the system completelyfilled with chilled injectate.

The system can be operated entirely automatically because of theelectrical connection between the combination 55 and the cardiac outputcomputer 56, as well as the electrical connection between the automaticsyringe drive assembly 10 and the cardiac output computer 56. After thecardiac output computer 56 receives a signal from the thermistor of thethermodilution catheter 58 (i.e. the temperature of the patient end ofthe thermodilution catheter 58 has stabilized) the signal to inject afirst chilled bolus is given by the cardiac output computer 56 to theautomatic syringe drive 10.

As described in connection with FIG. 1, there is a manual override forswitch 30 to activate the syringe drive 10. For fully automaticoperation a shunt between the switched connections from the power supply33 and the motor 34 will begin the operation of the automatic syringe10. This shunt can be provided by the cardiac output computer 56 for asufficient time to run the motor past the cam flat 21b and switch 30will then complete the circuit and run the motor 34 for one completecycle of the plunger 13.

Automatic plunger operation is qualified by the temperature of thechilled injectate which is measured in the chilled surface 46 of thethermoelectric chiller assembly. When that chilled surface 46 is at itsoperating temperature, the cardiac output computer 56 will start thecycle of the syringe drive assembly 10. The injection will be completedat the point where the movable contact 31 of switch 30 has again reachedthe cam flat 21b. The system is capable of manual operation. Thethermoelectric chiller and cassette having reached operatingtemperature, a medical practitioner can manually start the cardiacoutput computer 56, and then the automatic syringe drive 10. The systemwhen automatically or manually operated provides accurate and repeatablevolumes of carefully cooled injectate.

While a preferred embodiment has been shown and describe in connectionwith the automatic injectate system for a bolus of a preselected volume,those skilled in the art will no doubt appreciate that changes andmodifications can be made. The claims which follow seek to cover thebroad concepts of the unique heat exchanger used to adjust thetemperature of the bolus before injection and the simplified techniqueand mechanism designed to permit accurate and efficient change ofinjectate volumes in an automatic syringe drive mechanism.

What is claimed is:
 1. A thermoelectric device for rapidly changinginjectate temperature in a cardiac output thermodilution catheter systemwherein a bolus of an injectate passes through a heat exchangercomprising;a thermoconductive means made of an energy conductor having apair of major surfaces one of which surfaces is shaped to exchangeenergy and definitively configured to mount in intimate and maximumsurface contact with a source of heating or cooling energy having acomplimentary configuration for contact with the definitively configuredmajor surface, the contact for uniform, rapid and efficient heattransfer through the thermoconductive means, and fluid path means madeof a material more resistant to heat transfer and less conductive thanthe energy conductor of the thermoconductive means and associated withsaid other surface of said thermoconductive means to define a tortuouspassageway thereacross for providing contact with the bolus during itspassage prior to injection and for maintaining the bolus in intimateheat transfer relation with said thermoconductive means, the combinationof said tortuous passageway and said thermoconductive means sufficientto change the temperature of the injectate bolus volume.
 2. Thethermoelectric device of claim 1 wherein said fluid path means isadhered to said other surface by a hot melt adhesive.
 3. Thethermoelectric device of claim 1 wherein said fluid path means is athermoformed circuitous pathway.
 4. The thermoelectric device of claim 3wherein said circuitous pathway begins and ends with a connector whichis shaped to seal and terminate the pathway and provide a fluid passagetherethrough.
 5. The thermoelectric device of claim 1 wherein said onesurface is held in contact with a heating or cooling surface.
 6. Thethermoelectric device of claim 5 wherein said thermoformed circuitouspathway is held against said cooling surface by a resilient insulatingmember.
 7. The thermoelectric device of claim 6 wherein said resilientinsulating member is on a door of a housing for said heating and coolingsurface.
 8. The thermoelectric device of claim 5 wherein the onedefinitively configured major surface is substantially planar.
 9. Thethermoelectric device of claim 1 wherein the thermoconductive means is athin sheet of metal and the fluid path means is a formed sheet ofplastic, the assembly having a structure for supporting the definitivelyconfigured major surface.